It is known, for example, from the published Specification of British Patent Application No.: 7,928,416 (G.B. No. 2,036,541A) to provide a vent (hole) in an upper part of the wall of the vessel and to provide the switch assembly with a steam responsive actuating mechanism which is actuable by a bimetal device disposed adjacent to the vent so as to be subjected to steam issuing from the vessel via the vent. In this switch assembly, the electrical components, such as the switch contacts and the conductors connecting the switch contacts to the immersion heater device and to electrical input terminal pins, are located in a chamber adjacent to a head of the immersion heater device, which head extends through a lower aperture in the wall of the vessel, some distance below the vent. The electrical components are thus protected from exposure to dirt and water.
The steam responsive actuating mechanism extends a considerable vertical distance from adjacent the vent to the head, and is carried on a body of the switch assembly. This body also carries the electrical components and is mounted on the head so as to clamp a dry overload actuating mechanism to the head, so that the dry overload actuating mechanism is responsive to overheating of the immersion heater device to actuate the switch contacts. The body is an assembly comprising a vertically elongate main molding (on which the steam responsive actuating mechanism is mounted), and a carrier molding (on which the electrical components are mounted). The carrier molding can be fitted to the head to enable the immersion heater, dry overload responsive actuating mechanism and electrical components to be tested (prior to being fitted to the vessel and prior to the main molding being connected to the carrier molding).
However, some considerable skill is needed to assemble the vessel to ensure that the head is secured to the vessel in a predetermined position so as to locate the bimetal device in position adjacent the vent or hole and to locate the main molding in a position to receive an outer cover.
The skill required to assemble the vessel can be reduced by utilizing jigs to pre-align the vessel and immersion heater assembly, or by providing cooperating means on the head and vessel wall to ensure that the head is located properly prior to being secured in position, but such expedients are costly.